A series of feeding trials were conducted where different types of diets or diets formulated with graded levels of single nutrients or varying concentrations of specific ingredients were fed to RCS rats. The criterion of evaluation was the development of cataracts in the test animals. Results of these trials indicated cataract incidence is influenced by dietary constituents, at least in the rat. The use of fishmeal in the formulations of either purified or natural ingredient diets markedly increased cataract maturity. Increased dietary calcium concentrations also increased cataract incidence but to a lesser extent than the fishmeal.